As the old saw goes, a child can change your life in ways you never dreamed. For no one is this more true than those who live on the fringes of society — people who eat one meal wondering where the next is going to come from, and go to sleep every night not knowing where they’ll lay their heads tomorrow.

This landscape and the people who inhabit it are explored to bleak but brilliant effect in the new film “L’Enfant (The Child),” opening Friday at Market Street Cinema. The latest from the Belgian brother-directors Jean-Pierre and Luc Dardenne, it’s a heartfelt and thoughtful piece of cinema. Though it might move a bit slow for American audiences, it’s still a bittersweet little morsel, more character study than plot in the best way possible.

Jeremie Reinier plays Bruno, a homeless young criminal who — along with his gang of elementary-school-age thieves — considers anything and everything as the next possible score. This includes the infant son his girlfriend Sonia (Deborah Francois) presents him with soon after the title screen. After a few minutes of playing at a farce of domestic bliss — taking little Jimmy strolling around town in a stolen pram — one of Bruno’s shady confidantes tells him that there are people who will pay good money for a healthy child. The hesitation is only momentary, and soon he’s off to cash in on his bundle of joy, without Sonia’s knowledge. This greed-driven transaction, Sonia’s reaction to it, and Bruno’s attempts to get the child back form the backbone of the story, with Bruno growing from a kind of cash-obsessed cyborg into at least the semblance of a human being by the time the credits roll.

As with much of French cinema, a lot of screen time in “L’Enfant” focuses on just observing the characters in their natural habit as they work out problems. While the same subject matter — baby for sale, the need to get him back, and the aftermath — might well have ended up a Tarantino-esque thicket of fast-paced plot and counterplot in the hands of an American director, here the characters are allowed to have their quiet moments; those still little bits of film when you can hear the wheels of grief and regret creaking in their heads. While this approach leads to much less “action” onscreen, it does result in richer characters — people you can feel for, even if you don’t like what they’ve done.

While “L’Enfant” isn’t quite a popcorn movie, it is a finely wrought little portrait of desperation, greed and remorse. If you’re a fan of great cinema, see it soon.

WaterloggedFor those of you who like your tragedy over-easy — or, in this case, not-so-easy — we present “Poseidon,” the modern remake of the 1972 disaster-movie classic “The Poseidon Adventure.”

As in the original, the plot revolves around a group of luxury liner passengers who find themselves in a fight for their lives after their cruise ship takes a hit from a giant wave and capsizes. After the boat goes topsy-turvy, ex-New York Mayor Robert Ramsey (Kurt Russell) sets off to find his daughter in the ship’s disco, leading a group of threadbare survivors with him, including suicidal gay architect Richard Nelson (Richard Dreyfuss), single mother Maggie (Jacinda Barrett) and her kid Conor (Jimmy Bennett). Meanwhile, fighting Russell for control of the little group is professional gambler Dylan Johns (Arkansas native Josh Lucas), who comes up with the idea of heading for the ship’s bow thrusters as a way to get through the hull before the boat sinks.

While we are able — thanks to computer magic — to see a more convincing portrayal of a big ol’ ship getting smacked by a big ol’ wave, the results of “Poseidon” are not much more satisfying than the original “Poseidon Adventure.” In both, you get an ensemble cast of mostly soggy B-listers working their way through an upturned ship. The difference here is that you have to pay $8 to watch them do it, instead of the 99 cents you’d get the original for at Blockbuster.

With “Poseidon,” Kurt Russell obviously has supplanted an aging Harrison Ford as America’s Scowling Dad figure, with the scenes between him and “daughter” Amy Rossum adding the schmaltz that can’t be recreated from the original “Poseidon Adventure” without the resurrection of Shelley Winters. Lucas, meanwhile, cements his position as the poor man’s Val Kilmer here (we haven’t decided if that’s a compliment or not), and Dreyfuss just looks so damned old and sickly that this viewer was actually worried about his cardiovascular health in some of the more strenuous scenes. Faring better was Barrett, the young actress who lit up last year’s “Ladder 49” and who is set to make a big-screen splash in more than a handful of movies in the next year.

In short: Same ship, different day. Unless you’re a member of Josh Lucas’s immediate family and you have to see it so he won’t get his feelings hurt, rent the original and save yourself a few bucks.